Vascular smooth muscle cells are a vital component of the blood vessel wall, possessing extraordinary adaptive abilities. These cells display a range of phenotypes that are dependent upon the selective utilization of transcriptional programs. While smooth muscle modulation is essential for normal blood vessel function, their adaptive abilities are adversely associated with the pathologies of vascular occlusion diseases. Consequently, the molecular mechanisms governing gene transcription leading to resultant phenotypes are both biologically and clinically relevant. As an inroad to elucidating critical features that control smooth muscle transcription, our studies are focused on the development and differentiation of precursor cells into mature smooth muscle. Differentiation is accompanied by the orchestrated activation of a precise set of genes required for contraction. Though definitive regulatory elements, and corresponding transcription factors are recognized to have a role in differentiation, how they are coupled to signals that convey selective gene expression is not well understood. We hypothesize that extracellular signals, like transforming growth factor-beta (TGF-IS), use a distinct combination of intracellular pathways and transcription factors to impart smooth muscle-restricted expression. TGF-li has emerged as primary candidate for governing smooth muscle cell phenotypes. The aims of this proposal are designed to employ the smooth muscle-specific expression of the cysteine-rich protein 1 (CRP1) gene to investigate the cis-acting elements, and trans- acting factors that convey selective transcriptional activity in response to defined signaling events. We have identified a unique regulatory region of the CRP1 gene that drives expression exclusively in arterial smooth muscle cells. We intend to use this regulatory element to characterize essential transcriptional pathways important for the expression of the CRP1 gene in differentiated smooth muscle cells. The specific aims are: 1) To define the transcriptional mechanisms underlying the activation of the CRP1 gene by transforming growth factor-beta-1 (TOF-I^). 2) To determine the relationship between the functional activity of serum response factor (SRF), and signaling events that govern smooth muscle gene expression. 3) To unequivocally determine the necessity of the CArG element for expression of CRP1 by targeted mutagenesis. These studies are significant, as they will extend beyond the analysis of the transcriptional regulators, and determine the exact pathways that mediate transactivation, to address fundamental questions regarding the manifestation of smooth muscle cell phenotypes.